1. Field of the Invention
The invention relates to a semiconductor device, and more particularly, to an oxide semiconductor transistor with a U-shaped channel layer.
2. Description of the Prior Art
Attention has been focused on a technique for formation of a transistor using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, and within which, oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn) has been attracting attention.
A transistor including an oxide semiconductor film is known to have an extremely low leakage current in an off state. Nevertheless, current architecture of integrating transistor having oxide semiconductor film with metal-oxide semiconductor (MOS) transistor is still insufficient in bringing out optical performance of the device. Hence, how to improve the current fabrication flow for integrating oxide semiconductor transistor with MOS transistor has become an important task in this field.